Currently, to identify a Resident Space Object (RSO) (e.g., an operational satellite, an expended rocket body, or other space debris) as a specific known object, either the active participation of the satellite is required (e.g., via a radio transponder) or observations are compared against the previously known orbits of known RSOs. A space launch, even if completely successful, also usually results in multiple non-space vehicle objects in orbit, often with several items in quite similar orbits. The last stage of a rocket often gently releases one or more payloads and then may do little or nothing to actively separate from the payloads. As a result, a tight grouping of active satellites and expended rocket bodies, fuel tanks, and other debris are often created that should be distinguished during the first few orbits after launch. Some sets of satellites, even from different launches, are also specifically designed to operate together in a close constellation or to share the same orbital slot. Choosing the “wrong dot of light” to send radio commands to can imperil the mission.
Optical telescopes and radar systems can show the positions of multiple objects, but they do not necessarily determine which object is which. Objects in Low Earth Orbit (LEO), for example, can be observed for only a short time from any given ground station, and it may not be possible to match items even from one observation to the next. The optical characteristics (e.g., color, brightness, variability, etc.) may provide some information, but this is not always sufficient for identification.
Even after an RSO is properly identified, it must be frequently and continually re-observed to maintain track custody. An orbital maneuver must also be carefully observed to avoid losing track of the space vehicle. A major atmospheric disturbance, e.g., from a solar flare, can cause simultaneous perturbations to the orbits of many space vehicles, and it is not unusual for many space vehicle tracks to be lost or confused either temporarily or permanently. If an unknown RSO is detected, it is often impossible to tie it back to a previously known object, and without such knowledge, it is more difficult to predict its future orbit, leading to the possibility that the object will be lost again. Thus, once a space object is identified, it is necessary to make repeated measurements of every known object at a high enough frequency such that as the orbit changes, a new observation can be tied to the previously known object.
Known objects that are tracked can have their orbits predicted, allowing other operational space vehicles to dodge and avoid devastating collisions, or at least ascribe liability if they do collide. Tracked unknown objects can be less reliably predicted, and untracked objects can smash into valuable space assets without warning. For these reasons, it would be useful if every object that launched into space carried a beacon that can be read from the ground with low cost equipment and provide a unique and unambiguous identification even among closely spaced RSOs. This beacon should be small, simple, lightweight, durable, and autonomous so that one or more can be added to each desired component of a space launch without a significant engineering effort and without using up spacecraft resources.
Active satellite payloads often include radio transmitters to transmit data and communications to the ground as part of the space vehicle's primary purpose or for operations. These transmissions may be sufficient to identify a satellite, but if multiple satellites are in the beam of the ground antenna, this does not identify which vehicle is which. An unidentified satellite may be transmitting, but at an unknown frequency. A satellite may also leave its transmitter inactive until it receives a command to turn it on, which cannot be given without knowing which object it is.
Some satellites carry global positioning systems (GPS) or other navigation systems that allow the satellites to know their positions and transmit them to the ground, but most do not. Furthermore, this applies only to satellites that are actively transmitting. When a satellite reaches the end of its useful life, its transmitter is usually permanently disabled to prevent it from malfunctioning in the “ON” state and causing interference with intended communications. Inactive space debris, such as rocket bodies, have no transmitters at all.
If something goes wrong with a satellite, data regarding the event can help to recover the spacecraft. However, it is often the case that the malfunction includes a lack of communication, and all that is known on the ground is that the satellite went silent. Thus being able to receive additional state-of-health information about a satellite would be useful for analyzing spacecraft anomalies and recovery operations.
Effective identification is a terrestrial problem as well. The present state of the art for nighttime personnel identification as friend or foe (IFF) beacons is optically very similar to an infrared strobe light. Commonly available nighttime personnel IFF beacons are visible with night vision goggles. These personnel IFF beacons are intended to be invisible to adversaries, but are not. The night vision systems needed to see these personnel IFF beacons are now quite conventional and available worldwide. Accordingly, improved nighttime personnel IFF beacons may be beneficial. This need for improved nighttime IFF beacons includes those for personnel, objects, vehicles, units, equipment, locations, etc.